The Coombes Property Group wants to convert the Event Cinemas site on George Street into an apartment block soaring to 260 metres.

This would be 25 metres higher than what otherwise would be Sydney's tallest residential tower: the Greenland Centre, due to be completed in 2017.

The proposal would require changes to planning controls, which currently allow for two 150-metre towers at the George Street site, to instead accommodate the single, taller tower above a mixed-use podium.

A building of this size could include about 600 apartments.

A City of Sydney report recommends that the council support the proposal, which would also require state government approval.

All structures above 200 metres in central Sydney also fall within the airspace of Sydney airport and are subject to federal approval by Air Services Australia and CASA, a council spokeswoman said.

"The Events Cinema site has a height limit of 150-metres, but studies showed that a taller, thinner building was more preferable in this location given the proximity of its neighbours," she said.

"The proponent is offering to build two new childcare centres on the podium to help alleviate the shortage of child care in the southern area of central Sydney, which will be owned by the City."

Coombes bought the George Street cinema site from Challenger Financial Services Group in 2009 for $85 million. Mirvac is working with the company on the proposal.

Sydney Tower remains the city's tallest structure, at 309 metres.